An ammonite is a member of or a believer in the Ammon religion.
Ammonites believe that God is a giant, largely invisible mollusc that lives in heaven.
Ammonites further believe that all molluscs living on Earth today and any molluscs living on any other planet in the universe are each individually the direct creation of God. Just to make that clearer, they don’t believe that God created the molluscs species and then left reproduction to create individual molluscs. They believe that each and every mollusc is created individually by God at the time it comes into existence.
Ammonites also believe that all other living beings of any sort—whether plant, animal, bacterial or viral, other than molluscs—just kind of happened through an unknown process—possibly, but not necessarily evolution.
Ammon dietary laws strictly forbid the eating of molluscs, for they art holy. Eating anything else is perfectly fine by ammonites as long as it doesn’t kill you. Actually, eating something that will kill you is also OK with them. It’s just not recommended unless you’re a nonbeliever, in which case it’s encouraged.